Continuous casting process and apparatus



June 30, .1970 L. WATTS 3,517,725

CONTINUOUS CASTING PROCESS AND APPARATUS Filed Feb. 14, 1968 2 Sheets-Sheet 1 FIG. I

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LEONARD v WATTS ATTORNEY BY ow f w June 30, 1970 I L. WAT I'S I 3,517,725 I CONTINUOUS CASTING PROCESS AND APPARATUS Filed Feb. 14, 1968 v 2 sh e'e tsgsheet 24 LEONARD WATTS ATTORNEY United Patent 01 3,517,725 CONTINUOUS CASTING PROCESS AND APPARATUS Leonard Watts, Cedarlrurst, N.Y., assignor to Technicon Corporation, Tarrytown, N.Y. Filed Feb. 14, 1968, Ser. N 0. 705,491 Int. Cl. B22d 11/08, 11/10 U.S. Cl. 16482 10 Claims ABSTRACT on THE DISCLOSURE BACKGROUND OF THE INVENTION In the normal continuous casting of steel, an open water cooled mold is maintained in a fixed vertical position while a billet being cast is withdrawn from below it at a rate determined by thermodynamic conditions. The continuously cast billet is then cut into length for further processing.

The elevation required for conventional continuous casting apparatus requires considerable costs for construction to raise the molten steel to a required height. The continuous casting apparatus of this invention allows the substantially horizontal continuous casting of steel with resulting savings. Further, the process of this invention may allow for the continuous casting of rimmed steel as sufiicient time for the escape of entrained gases may be allowed.

SUMMARY OF THE INVENTION A closed end water cooled mold is withdrawn from about a hollow or tubular starting bar protruding from a tundish. Molten metal solidifies on contact with the mold walls, however, the molten metal is longer in contact with the longitudinally sliding side walls which form a solidified tubular shell about a core of molten metal. As metal solidifies on its brief contact with the end wall of the mold and the mold is withdrawn, the thin solidified end wall ruptures and remelts. This continues as the billet is continuously cast. Thus a billet, according to this invention, is formed from its end remote from the tundish with molten metal flowing through the length of the billet as it is formed. The mold may be withdrawn in a series of incremental steps or oscillations to assist in the continuing remelting of the end wall. Further, a billet may be formed horizontally or inclined downwardly to allow for the escape of entrained gases.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is a longitudinal, vertical section through a continuous casting apparatus at the start of a cast according to this invention;

FIG. 2 is a longitudinal, vertical section through a fragment of the exit nozzle of a tundish, a starting bar, a billet in process of being cast, and a differentially cooled mold;

FIGS. 3 and 4 are longitudinal, vertical sections through modifications of water cooled molds;

FIG. 5 is a longitudinal, vertical section through a mold and a fragment of an ingot being cast therefrom, the mold being modified to inject a lubricant therein;

FIG. 6 is a longitudinal, vertical section through a mold and a fragment of an ingot being cast therefrom 3,517,725 Patented June 30, 1970 with side walls of the billet being shown sprayed with water on emergence from the mold and with a solidified end wall of the billet being shown therein;

FIG. 7 is a longitudinal, vertical section through a mold and a fragment of a billet being cast therefrom showing the solidified end wall of a billet out of contact with the end wall of the mold prior to rupturing and remelting of the billet end wall;

FIG. 8 is a longitudinal, vertical section through a tundish, a billet being cast, and a mold showing a modification of this invention in which a billet is east at an angle with the horizontal; and

FIG. 9 is a side view of a tundish and a longitudinal, vertical section through an unattached starting bar and a fragment of a billet with molten metal shown flowing from the tundish into the upper end of the starting bar as the billet is being cast.

DESCRIPTION OF THE PREFERRED EMBODIMENT FIG. 1 shows a casting ladle 10 from which a hot metal stream 11 flows into tundish 12 which is lined with any suitable heat resisting material 13. Tundish 12 has a stopper rig 14 to allow controlled flow of molten metal 15 through nozzle .16. The tubular or hollow starting bar 17 is fixed to nozzle 16 and the starting bar 17 has an outer tapering end 18 containing peripheral grooves 19. The tapering end 1 8 of starting bar 17 is disposed in the closed end mold 20 which is of copper and water cooled.

Tundish 12 rests on base 19 from which tracks 21 extend to support a mold transport carriage 22 on wheels 23. Carriage 22 has mold 20 resting thereon connected to a mold oscillator 24 by means of rod 25. Carriage 22 is drawn to the right as shown by bar 26 as a billet is cast. Billet supports 27, shown in lowered positions, are raised to support a billet as it is cast and the mold 20 moves to the right. Cooling water 28 enters mold 20 through hose 29 and leaves through hose 30.

Referring now to FIGS. 1, 6, and 7, a billet 32 is cast in the following manner. Molten steel from tundish 12 flows through the hollow starting bar 17 into the closed end mold 20. Starting bar 17 may be pre-heated to prevent excessive solidification of steel therein which would block further flow of steel through the starting bar. The liquid steel striking the water cooled mold 20 solidifies around the tapered end 18 of bar 17 and adheres to bar 17 assisted by the grooves 19. Holes or projections from the starting bar may alternately be provided to enable a solidifying steel shell to adhere to it. Chill scrap may also be provided to ensure quick and positive solidification around the tapered end 18 of bar 17.

As soon as the mold cavity 33 is filled with molten steel, the transport carriage 22 and the mold 20 is moved to the right as shown. As may be seen in FIGS. 6 and 7, a solidified casting shell 34 is formed with a molten core or center 35. As the mold 20 moves to the right, molten metal continues to flow from the tundish 12 through the molten center 35 of billet 32 to be solidified and form casting shell 34 at the end of the billet remote from the tundish 12. Although a thin end membrane 36 may form as the molten steel contacts the cooled end wall 37 as shown in FIG. 6, further movement of mold 20 away from the tundish 12 will move end wall 37 away from the thin membrane 36 as shown in FIG. 7. Molten steel of core 35 Will then rupture and remelt membrane 36.

The side walls 38 of mold 20 have a longer sliding contact with the casting shell 34 so that it cools and solidifies to resist ferrostatic pressure. As mold 20 moves away from tundish 12, nozzles 40 direct a water spray 41 as needed on the casting shell 34. As in conventional continuous casting, the casting shell 34, on solidifying, will shrink away from the mold walls 38. If desired, the

mold walls 38 may be tapered slightly'toward'the open end of mold 20 to more closely follow the shrinking casting shell 34.

Referring further to FIGS. 1, 6 and 7, a mold oscillator 24 may be connected to mold 20. The mold oscillator 24 advances the mold 20 in discrete steps to produce a physical gap between the cooled end wall 37 and the end memberance 36 of solidified steel. The end membrane 36 is in a plastic state and is unable to withstand even the small ferrostatic pressure acting on it. In addition, the mass of membrane 36 compared with the volume of liquid metal in contact with it is very small. The combined effects of this pressure and heat cause the membrane to rupture and remelt almost instantly. Liquid metal will now fill the gap shown between membrane 36 and end wall 37 as shown in FIG. 7.

To assure the continued formation and remelting of the membrane 36, the mold 20 should be oscillated in a particular manner. If it is assumed that the mold transport carriage is being moved away from the tundish 12 at a casting rate of 36 inches per minute, the mold should be oscillated at a rate less than 36 inches per minute for a given number of cycles per second which, for example, could be ten cycles per second. If the mold oscillator 24 moves the mold 20 on carriage 22 at a speed of 36 inches per minute, the mold 20 will remain stationary relative to billet 32 for a short period of time and then move away from tundish 12 with a velocity of 72 inches per minute for a short period of time. While the mold 20 is stationary relative to billet 32, the membrane 36 will form.. When the mold 20 is moved away from tundish 12, the membrane 36 will remelt. The amplitude and period of oscillation of mold 20, if required, may be determined by the length of time required for the formation and remelting of membrane 36.

Certain emperical formulas have proven to be reasonably accurate to determine the length of time required for a continuously cast slab or billet to solidify completely. Such a formula for a slab is T =.l7d where d is a slab thickness in inches and T is time in minutes. Thus a inch thick slab will solidify in 17 minutes. This formula takes into account that a portion of the slab thickness has solidified in a continuous casting mold and that maximum external cooling as by water spray is provided. It is quite reasonable to assume that, with less spray cooling except where absolutely required, as at the mold exit, and with the continuous addition of heat by the flow of molten metal in the core 35, solidification may be extended well past 60 minutes in core 35 through the length of an ingot or billet being cast according to this invention. Based on the rate of conventional continuous casting speeds, 60 minutes is adequate time to completely empty a ladle of average size. Thus the process of this invention appears to be thermodynamically feasible.

FIG. 2 shows a billet 32 having a casting shell 34 and a molten core 35 being cast in a mold 20" having differential cooling therein. Billet supports 27 have been raised to support the length of billet 32 as it is being formed. Water spray nozzles 43 direct a spray 44 on the casting shell 34 as it emerges from mold 20'.

Mold 20 is divided into two water compartments 45 and 46 which cool the mold side walls 47 and a water compartment 48 which cools the end wall 49. Cooling water inlet tube 29' branches into the tubes 50, 51 and 52 which enter the compartments 45, 46, and 48, respectively. By means of the valves 53, 54, and 55 cooling in different portions of the mold 20' may be increased or decreased as required. Water leaving the mold 20' passes through the tubes 56, 57, and 58.

FIGS. 3, 4, and 5 show modifications of molds according to this invention. Mold 60 has an end wall 61 which curves smoothly from the side walls 62. Mold 63 has an end wall 64 that is concave. Mold 65 has an inlet passage 66 in its end wall 67 through which a mold lubricant may be injected from tube 67' as mold 65 moves to'the right leaving a gap between membrane 36 and mold wall 67. Oxygen may also be injected to assist in rupture of membrane 36 by generation of heat.

It is to be noted that when horizontal continuous casting is carried out according to this invention, the ferrostatic pressure in the casting shell 34 is very low so that the casting shell 34 need only be cooled to solidify sufiiciently to contain this low ferrostatic pressure. If billets 12 by 15 inches were continuously cast according to this invention, they should be able to be cast for or more feet in length. On completion of the casting of a billet 32, the mold would be stopped for a period to solidify an end wall 36 of a billet which would be thick enough to resist ferrostatic pressure in the molten core 35. The completed billet would then be further cooled for complete solidification.

It has been particularly difficult for conventional continuous casting apparatus to cast rimmed steel because liquid rimmed steel is extremely gaseous and the conventional apparatus does not allow for the release of this gas on solidification. This unreleased gas causes imperfections which render the product unusable as high quality sheet after rolling.

As shown in FIG. 8, tundish 12 has a stopper rig 14' and an inclined nozzle 16. From nozzle 16', by means of a hollow starting bar (not shown), a billet 70 is cast at an angle a with the horizontal as indicated by the arrow 72. While continuous casting at an angle with the horizontal increases ferrostatic pressure on the solidified billet wall 73, it allows gases to escape upward.

A further modification is shown in FIG. 9 in which a tundish 12" has a spout 75 which delivers a stream 76 of controlled flow of molten metal 77 into the upper end of an open starting bar 78. The upper end of starting bar 78 may be surrounded by insulation 79 to prevent solidification of molten metal therein. Billet 70 is thus formed as hereinbefore described at an angle with the horizontal to allow the ready escape of gases as when casting rimmed steel. Heat may be added to the upper end of the billet 70 after casting to prolong the length of time in which gases may escape fro mthe molten core.

If desired, mold may be spring mounted on carriage 22 to be rapidly jerked away from tundish 12 along billet 32 if the mold seizes momentarily to the billet. The method and apparatus for continuous casting herein described may be applied to other metals than steel.

While this invention has been shown and described in the best form known, it will nevertheless be understood that this is purely exemplary and that modifications may be made without departing from the spirit and scope of the invention except as it may be more limited in the appended claims wherein:

What is claimed is:

1. The process of continuously casting a metal billet or slab comprising the steps of:

(a) introducing molten metal from a source of molten metal into a cooled, closed end mold, and

(b) relatively withdrawing the closed end mold at an average casting speed from the source of molten metal forming a solidified casting shell of a billet with a molten core, molten metal from the source of molten metal flowing through the core of the billet toward the closed end mold during casting.

2. The process according to claim 1 wherein the billet is continuously cast of steel.

3. The process according to claim 2 wherein the mold is intermittently withdrawn so that an end wall of the closed end mold forms a solidified end membrane of the billet, the end membrane being remelted on each with- V drawal of said mold.

billet or slab comprising, in combination:

apparatus is for the continuous casting of a steel billet or slab and wherein the mold is water cooled.

6. The process according to claim 2 wherein molten steel from the source of molten steel is introducd into the mold through a tubular starting bar about which the mold extends, the casting shell solidifying to the starting bar.

7. Apparatus for the continuous casting of a metal (a) a source of molten metal,

(b) a tubular starting bar through which molten metal is introduced from said source of molten metal,

(0) a cooled closed end mold having side walls and 10 an end wall, said mold being disopsed about said starting bar, and

((1) means for relatively withdrawing said mold from said starting bar in such a manner as to cause molten metal to flow through said starting bar to said mold and form a billet with a molten core and a solid casting shell which forms on contact of said molten core with said wall structure of said mold.

8. The combination according to claim 7 wherein the 9. The combination according to claim 8 wherein said 6 10. The combination according to claim 8 wherein said means withdrawing said mold withdraws said mold intermitttently so that the end wall of said mold forms a solidified end membrane of the billet, the end membrane being remelted on each withdrawal of said mold.

References Cited UNITED STATES PATENTS 1,808,370 6/1931 Munson 164--274 2,369,233 2/1945 Hopkins 16482 X FOREIGN PATENTS 67,015 5/1957 France. 1,160,525 7/1958 France.

747,349 9/ 1944 Germany. 763,224 12/ 1952 Germany.

20 J. SPENCER OVERHOLSER, Primary Examiner R. S. ANNEAR, Assistant Examiner US. Cl. X.R. 

